Hybrid air-conditioning system and method of operating the same

ABSTRACT

A hybrid air-conditioning system for controlling the condition of air in a building-enclosed space includes a first fan for passing process air from an ambient space through a first pre-cool evaporator coil, through a first zone of a rotatable moisture transfer wheel and then through a first zone of a rotatable heat exchange wheel to an enclosed and conditioned space. A second fan passes regenerative air from the enclosed and conditioned space through a second zone of the heat exchange wheel, through a first condenser coil, through a second zone of the moisture transfer wheel and then to the ambient space. The system further includes first and second compressors. The first compressor is in fluid communication with the first pre-cool evaporator coil and with the first condenser coil. The second compressor has a suction side in fluid communication with a second pre-cool evaporator coil and with a second condenser coil. The second condenser coil has first and second coil sections, with the first coil section of the second condenser coil positioned between the first condenser coil and the second zone of the moisture transfer wheel and the second coil section of the second condenser coil positioned between the second zone of the moisture transfer wheel and the ambient space.

This application is a continuation-in-part of U.S. application No.08/378,154, filed on Jan. 25, 1995.

FIELD OF THE INVENTION

The present invention relates to a hybrid air-conditioning system and,more particularly, to an air-conditioning system which utilizes thecombination of an electric heat pump and regenerative type periodic flowdevice for conditioning air within an enclosed space wherein the airwithin the enclosed space is exhausted from the enclosed space at arelatively high rate.

BACKGROUND OF THE INVENTION

Regenerative type periodic flow devices are conventionally employed forthe transfer of heat or of other constituents from one fluid stream toanother, and thereby from one area or zone in space to another.Typically, a sorptive mass is used to collect heat or a particular masscomponent from one fluid stream which flows over or through the sorptivemass. The flowing fluid is rendered either cooler (in the case of heatsorption) or less concentrated (in the case of, for instance, adsorptionof particular gases). The sorptive mass is then taken "off-stream" andregenerated by exposure to a second fluid stream which is capable ofaccepting the heat or material desorbed with favorable energetics.

In many instances, the sorptive material is contained within a vessel ordistributed within a bed structure. It is desirable that such materialbe provided with maximum surface area, and that the fluid flow throughthe sorptive material matrix in a smooth (non-turbulent) and regularstate. Once the sorptive material has been saturated (i.e., has reachedits maximum designed capacity for sorption), the vessel or bed is thenremoved from the fluid flow path and exposed to a second fluid flow toregenerate the sorptive capacity of the material by, for instance,cooling the sorptive material or desorbing material taken up during"on-stream" operation. After such regeneration, the sorptive material isonce more placed back "on-stream" and the operation continues.

From such single cycle systems evolved multiple vessel systems whichpermitted semi-continuous (or semi-batch) operation by synchronouslyalternating two or more sorptive vessels between on-stream andoff-stream operation. The choice of numbers of vessels and cyclestructures depends on many factors, but most importantly the ratiobetween consumption rate of the sorptive capacity of the vessel, andregeneration rates for that same vessel.

In some applications, semi-continuous systems have evolved intocontinuous flow systems where the sorptive media itself is moved betweentwo or more flowing fluid streams. The most common construction employedfor such systems is a porous disk, often referred to as a wheel orrotor. In its simplest form, such a wheel is divided into two flowzones, and fluid is passed over the sorptive surface of the wheel(typically flowing through the thickness of the disc parallel to therotational axis of the cylinder) as the wheel is rotated to carry thesorptive material from one zone, into the other, and back again tocomplete a revolution. In a heat exchanger wheel, for instance, one zoneof warm fluid and one zone of cooler fluid are present. Heat is adsorbedby the material of the wheel in the warm flow zone, and is carried awayfrom the wheel as the sorptive material passes through the cool flowzone. U.S. Pat. No. 4,594,860 discloses such a continuous flow systemand is hereby incorporated by reference.

FIG. 1 illustrates a schematic of a conventional open-cycleair-conditioning system, generally designated 9. A moisture transferwheel assembly 11 constitutes the exterior or outside element of thesystem 9. As discussed hereinafter, the moisture transfer wheel 11 isseparated into two sections to provide an intake path and an exhaustpath through the moisture transfer wheel 11, as indicated by the arrows.A heat exchanger wheel assembly 13, also partitioned to provide intakeand exhaust paths, is located substantially adjacent to the moisturetransfer wheel 11, separated only by a heat regeneration coil 19. Anauxiliary heating coil 21 may be placed in the system 9 for use in coldmonths when it is desirable to heat the interior of the area to beconditioned, rather than to cool it. The heat regeneration coil 19 andheating coil 21 include fluid pipes (not shown) which are interconnectedwith standard heating units (not shown), such as a solar heating unit.The system 9 terminates in a pair of evaporator elements 15 and 17separated by a partition 6 with the arrows indicating the intake airinto the building and the air exhausting therefrom. A supply blower 23and an exhaust blower 25 are provided to implement the necessary airmovement within the system.

As is well known, the system 9 provides removal of the moisture from theintake air by the moisture transfer wheel 11. When moisture is removedfrom the air, the temperature of the air increases. The air issubsequently cooled upon passing through heat exchanger wheel 13, whichlowers the temperature of the warm, dry air. Evaporator element 15 addsmoisture to the air, thus reducing the temperature further and supplyingcool air to the conditioned area. The exhaust air passes throughevaporator element 17 and through heat exchanger wheel 13 to remove heatfrom the heat exchanger and raise the temperature of the exhaust air.The temperature of the exhaust air is further raised by means of theheat regeneration coil 19 to provide high temperature air in the exhaustpath, resulting in regeneration of the moisture transfer wheel 11. Theair from the moisture transfer wheel 11 is exhausted into theatmosphere. The system 9 is disclosed in U.S. Pat. No. 4,594,860,accordingly, further description of the structure of the system 9 isomitted for purposes of brevity only, and is not limiting.

There is a temperature relationship between the process or intake airleaving the moisture transfer wheel 11 and the required regenerationtemperature of the regeneration or exhaust air entering the moisturetransfer wheel 11. The temperature of the regeneration air entering themoisture transfer wheel 11 needs to be high enough to create a vaporpressure which is lower than the vapor pressure of the process airleaving the moisture transfer wheel 11, which is then moved to the heattransfer wheel 13. The regeneration air entering the moisture transferwheel 11 also needs to have enough sensible energy for the condensedwater trapped in the moisture transfer wheel 11 to vaporize and freeitself from the moisture transfer wheel 11. In the past, the temperatureof the regeneration air entering the moisture transfer wheel 11 wasrequired to be a minimum of forty degrees Fahrenheit higher, and as muchas one-hundred-and-fifty degrees Fahrenheit higher than the temperatureof the process air leaving the moisture transfer wheel 11 toward theheat transfer wheel 13.

Where the moisture transfer wheel 11 can regenerate at a relatively lowtemperature, for instance, one-hundred-and-forty degrees Fahrenheit, themoisture transfer wheel 11 has the advantage of using waste heat fromconventional air-conditioning and refrigeration condensers, among othersources. However, where the moisture transfer wheel 11 can regenerate atrelatively low temperatures, there is a problem with treating processair which is drawn from ambient conditions which has the potential ofbeing both high in temperature and humidity. Hot ambient temperatureslimit the amount of moisture that can be removed from the incomingprocess air because the process air leaving the moisture transfer wheel11 has to have a lower temperature than the regeneration temperature. Asthe process air passes through the moisture transfer wheel 11, thelatent heat of vaporization is released by the water vapor beingwithdrawn from the air and, as a result, the air picks up the latentheat. The released latent heat increases the air temperature at arelationship of about 0.62 degrees-per-grain of moisture removed. Whentreating ambient air which is both high in temperature and humidity,less moisture can be absorbed by the moisture transfer wheel 11 andconverted to sensible temperature before the process air begins toapproach the regeneration temperature limit. Thus, the system will reachsome equilibrium at a much-reduced latent capacity. Thus, a need hasarisen for a regenerative-type air-conditioning system which can processambient air which is both high in temperature and moisture withoutreducing the latent capacity of the system.

While the foregoing problem of not being able to treat process air whichis derived from one-hundred-percent ambient air has been solved in thepast by taking the process air from within the space to be conditioned(i.e., a recirculation unit), the use of a recirculation unit cannotmeet the demands of all air-conditioning applications. For instance,where the space to be conditioned includes a supplemental relativelyhigh volume exhaust system, such as in a commercial kitchen having largeexhaust fans for removing air and smoke from the cooking area. In suchan application, a recirculation unit would not meet the demand forreplacing air within the enclosed space. As a result, a negativepressure would be created within the space to be conditioned therebycausing ambient air to enter the space to be conditioned whenever a dooror window is opened.

The heat regeneration coil 19 and heating coil 21 of the system 9 are ofconventional structure. That is, in conventional coil arrangements, thetubing is mechanically connected to fin sheets. The fin sheets are usedto extend the surface area of the tubes to increase the coil'sheat-transfer effectiveness. That is, a typical condenser or coolingcoil is made up of finned tube sheets with good transfer conductionmaterial, typically aluminum or copper, with holes punched in a patternarray through which the tubes are inserted. Through various means, thetubes are expanded to make good contact with the finned tube sheets. Ina typical application, air passes over the tubes and fins and is eithercooled or heated by the fluid flowing inside the tubes.

Since heat is conducted not only to the area that passes over the finsheets, but from the warmest area on the finned surface to the coolestarea on the finned surface, because of the high conduction of finsheets, the fin sheets tend to average out the temperature across thecoil, even though the fluid in the tube is at different temperaturesbetween front and back. Thus, the upper and lower temperature limits towhich the air can be heated or cooled is therefore limited, whichdirectly affects the total heat transferred by the coil and the energyefficiency of the system 9. Thus, a need has arisen for a condensing orcooling coil which can minimize the effect of averaging out thetemperature across the coil without losing the benefit of the use of finsheets.

The present invention solves the foregoing problems by pre-cooling theprocess air entering the moisture transfer wheel and separating thecoils into two sections. By knowing the performance of the moisturetransfer wheel at various dew points, the process air entering themoisture transfer wheel could be cooled to a specific dew pointdepending on the desired leaving-air humidity. Pre-cooling the processair entering the moisture transfer wheel increases the total moistureremoved by the moisture transfer wheel 11 because the process airentering the moisture transfer wheel 11 could handle a greater increasein temperature (due to the latent heat of vaporization) beforeapproaching the regeneration temperature limit. Separating thecondensing coils into two sections spaced by an air gap minimizes theaveraging effect by preventing heat transfer across the fin sheetsbetween the two sections. Use of the present invention results in ahybrid air-conditioning system which can process one-hundred-percentambient air, regardless of its temperature, in an energy-efficientmanner.

In order to increase efficiency at higher incoming regenerative airtemperatures, it has also been found to be more efficient to operate twoindependent, closed systems with a refrigerant fluid with independentcompressors. Optimal placement of the separated condensing coils fromeach system and the relative positioning of the pre-cool evaporatorsresults in increased system efficiency and performance.

SUMMARY OF THE INVENTION

Briefly stated, the present invention comprises a hybridair-conditioning system for controlling the condition of air in abuilding enclosed space. The system includes a first fan for passingprocess air from an ambient space through a first pre-cool evaporatorcoil, through a first zone of a rotatable moisture transfer wheel andthen through a first zone of a rotatable heat exchange wheel to anenclosed and conditioned space and a second fan for passing regenerativeair from the enclosed and conditioned space through a second zone of theheat exchange wheel, through a first condenser coil, through a secondzone of the moisture transfer wheel and then to the ambient space. Thesystem further includes first and second compressors. The firstcompressor has a suction side in fluid communication with a first sideof the first pre-cool evaporator coil and a discharge side in fluidcommunication with a first side of the first condenser coil. A secondside of the first pre-cool evaporator coil is in fluid communicationwith a second side of the first condenser coil. The second compressorhas a suction side in fluid communication with a first side of a secondpre-cool evaporator coil and a discharge side in fluid communicationwith a first side of the second condenser coil. The second condensercoil has a second side in fluid communication with a second side of thesecond pre-cool evaporator coil. The second condenser coil has first andsecond coil sections, with the first coil section of the secondcondenser coil being positioned between the first condenser coil and thesecond zone of the moisture transfer wheel and the second coil sectionof the second condenser coil being positioned between the second zone ofthe moisture transfer wheel and the ambient space such that theregenerative air passes through the first and second sections of thesecond condenser coil.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing Summary, as well as the following Detailed Description ofPreferred Embodiments, will be better understood when read inconjunction with the appended drawings. For the purpose of illustratingthe invention, there is shown in the drawings embodiments which arepresently preferred. It should be understood, however, that theinvention is not limited to the precise arrangements andinstrumentalities shown. In the drawings:

FIG. 1 is a diagrammatic perspective view of a conventional hybridair-conditioning system;

FIG. 2 is a schematic view of a hybrid air-conditioning system inaccordance with a first preferred embodiment of the invention;

FIG. 3 is a greatly enlarged cross-sectional view of a core of amoisture transfer wheel used in the air-conditioning system shown inFIG. 2;

FIG. 4 is an enlarged front-elevational view of the moisture transferwheel rotatably supported within a housing;

FIG. 5 is an enlarged cross-sectional view of the moisture transferwheel shown in FIG. 4 taken along lines 5--5 of FIG. 4;

FIG. 6 is a greatly enlarged cross-sectional view of the moisturetransfer wheel and housing shown in FIG. 4 taken along lines 6--6 ofFIG. 4; and

FIG. 7 is a schematic view of a hybrid air-conditioning system inaccordance with a second preferred embodiment of the invention.

FIG. 8 is a schematic view of a hybrid air-conditioning system inaccordance with a third preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Certain terminology is used in the following description for convenienceonly, and is not limiting. The words "right,""left," "lower" and "upper"designate directions in the drawings to which reference is made. Thewords "inwardly" and "outwardly" refer to directions toward and awayfrom, respectively, the geometric center of the hybrid air-conditioningsystem and designated parts thereof. The terminology includes the wordsabove-specifically mentioned, derivatives thereof and words of similarimport.

Referring now to the drawings in detail, wherein like numerals are usedto indicate like elements throughout, there is shown in FIGS. 2 through6 a first preferred embodiment of a hybrid air-conditioning system,generally designated 10, for controlling the condition of air in abuilding-enclosed space (not shown). Referring now to FIG. 2, the system10 includes first means for passing process air, represented by thearrow 51, from an ambient space (not shown) through a first pre-coolevaporator coil 50, through a first zone 52a of a rotatable moisturetransfer wheel 52 and then through a first zone 54a of a rotatableheat-exchange wheel 54 to an enclosed and conditioned space (not shown).In the first preferred embodiment, the first means for passing processair from the ambient space through the system 10 is a fan or blower 56.The fan 56 draws one-hundred-percent air from ambient conditions andpasses it through the system 10, as described hereinafter. Thus, in thefirst preferred embodiment, the system 10 of the present invention doesnot recirculate any of the air from within the enclosed and conditionedspace. However, it is understood by those of ordinary skill in the artfrom this disclosure, that the system 10 could be used as arecirculation unit or as unit which processes both recirculated andambient air.

In the first preferred embodiment, the fan 56 is preferably positionedupstream from the first pre-cool evaporator coil 50 directly adjacentthereto. However, it is understood by those skilled in the art from thisdisclosure that the fan 56 could be positioned upstream from the firstpre-cool evaporator coil 50 at a significant distance therefrom, usingconventional ducts (not shown). While it is preferred that the firstmeans for passing process air from the ambient space through the system10 be comprised of a fan 56, it is understood by those of ordinary skillin the art from this disclosure that other devices could be used to passair through the system 10, such as through the use of negative orpositive pressure zones.

The system 10 further includes second means for passing regenerativeair, generally designated by the arrow 58, from the enclosed andconditioned space through a second zone 54b of the heat-exchange wheel54, through a first condenser coil 60, through a second zone 52b of themoisture transfer wheel 52 and then to the ambient space. The secondmeans for passing the regenerative air 58 from the enclosed andconditioned space through the system 10 to the ambient space preferablyis comprised of a fan or blower 62, generally identical to the fan 56described above. The fan 62 for moving regenerative air 58 through thesystem 10 is located downstream from the second zone 52b of the moisturetransfer wheel 52 either adjacent thereto or a distance therefrom, butin fluid communication therewith, using ducts (not shown).

The rotatable moisture transfer wheel 52 constitutes the exterior oroutside element of the system 10. As discussed in more detailhereinafter, the moisture transfer wheel 52 is separated into twosections to provide an intake path (i.e., for the process air 51) and anexhaust path (i.e., for the regenerative air 58) through the moisturetransfer wheel 52. The heat exchange wheel 54 is also partitioned toprovide intake and exhaust paths, and is located substantially adjacentto the moisture transfer wheel 52, separated only by the first condensercoil 60. The moisture transfer wheel 52 and heat exchange wheel 54 arerotatably supported within a housing (not shown), described in moredetail hereinafter, which includes a partition, represented by the line63, which coincides with the partitioning of the moisture transfer andheat exchange wheels 52, 54 to thereby divide the system 10 into anintake path (hereinafter referred to as the "process side") having thefirst zones 52a, 54a of the moisture and heat exchange wheels 52, 54 andfirst pre-cool evaporator 50 therein and an exhaust path (hereinafterreferred to as the "regenerative side") having the second zones 52b, 54bof the moisture transfer and heat exchange wheels 52, 54 and firstcondenser coil 60 therein.

Generally, the operation of the moisture transfer and heat exchangewheels 52, 54 is well known. That is, the system 10 provides removal ofthe moisture from the process air 51 by the moisture transfer wheel 52.When moisture is removed from the process air 51, the temperature of theprocess air 51 increases. The process air 51 is subsequently cooled uponpassing through the heat exchange wheel 54, which lowers the temperatureof the warm, dry air. An evaporator element (not shown) may bepositioned on the process side downstream of the first zone 54a of theheat exchange wheel 54 to reduce the temperature further and supply evencooler air to the enclosed and conditioned space. The regenerative air58 flows over an evaporator pad 61 and then through the second zone 54bof the heat exchange wheel 54 to remove heat from the heat exchangewheel 54 and raise the temperature of the regenerative air 58. Theevaporator pad 61 lowers the dry bulb temperature of the regenerativeair 58 to the regenerative air's 58 wet bulb temperature in the range ofabout 65 to 80 degrees F., depending upon whether the regenerative air58 is drawn from the building enclosed space or from atmosphere.Lowering the wet bulb temperature of the regenerative air entering theheat exchange wheel 54 assists in removing heat from the heat exchangewheel 54. The temperature of the regenerative air 58 exiting the heatexchange wheel 54 is further raised by the first condensing coil 60, asdescribed in more detail hereinafter, to provide high temperatureregenerative air 58 on the regenerative side of the system 10 justupstream from the second zone 52b of the moisture transfer wheel 52,resulting in regeneration of the moisture transfer wheel 52 as theregenerative air 58 passes therethrough. The regenerative air 58 thenpasses from the moisture transfer wheel 52 into the atmosphere.

Two elements of the system 10 which contribute to the coefficientperformance (COP) of the system 10 are the moisture transfer wheel 52and the heat exchange wheel 54. With the exception of the specificmaterial used in these wheels, they may be constructed in substantiallythe same manner.

Referring now to FIGS. 3-6 and turning now to the construction of themoisture transfer wheel 52, the moisture transfer wheel 52 is rotatablymounted within a housing 38, as illustrated in FIG. 4. The moisturetransfer wheel 52 comprises a core 64 and a rim 34. The core 64 iscomprised of a plurality of adjoining parallel channels 14, asillustrated in FIG. 3. According to a preferred embodiment of the core64, each of the channels 14 is generally in the form of a hexagon incross section and includes an internal surface area 16. It is alsopreferred that the channels 14 be formed from a plurality of stackedlayers of material 12. The layers of material 12 of the channels 14 havea minimum thickness to inhibit the effect of the wall thicknessincreasing the pressure drop through the core 64 and yet provide thecore 64 with sufficient structural integrity to be self supporting. Inthe first preferred embodiment, it is preferred that the layers ofmaterial have a thickness of about 0.0015 inches. It is understood bythose skilled in the art from this disclosure that the exact thicknessof the walls formed by the layers of material 12 could vary, dependingupon the particular application of the core 64 and existingmanufacturing techniques, without departing from the spirit and scope ofthe invention. For instance, the thickness of the walls formed by thelayers of material 12 could be in the range of about 0.001 to 0.006inches.

Each of the channels 14 includes a centrally disposed longitudinal axis18. The channels 14 are preferably sized such that a distance betweenand along longitudinal axes of adjacent channels is generally uniform(i.e., the adjacent channels 14 are equidistantly spaced from each otherand extend generally parallel with respect to each other). In the firstpreferred embodiment, it is preferred that the distance between thelongitudinal axes 18 be in the range of about 0.050 to 0.125 inches.Thus, the channels 14 of the present invention, due to their hexagonalcross-sectional configuration, are closely adjoined to increase theavailable transfer surface per unit of volume.

In the present embodiment, it is preferred that the layers of material12 be comprised of a non-metallic, high-strength, temperature-resistant,low thermal conductivity material, such as Nomex<< aramid in paper form.The process of assembling the layers of material 12 in the form of thechannels 14 is well understood by those skilled in the art. An exampleof a commercially available product which meets the criteria of thepresent invention is Aeroweb<< HMX-20 without the resilient resincoating, manufactured by Ciba Composites of Anaheim, Calif., a divisionof Ciba Geigy Corporation of Ardsley, N.Y. However, it is understood bythose skilled in the art from this disclosure that the layers ofmaterial 12 and the manner in which they are formed are not pertinent tothe present invention, and that other materials, such as kraft paper,nylon fiber paper, mineral fiber paper and the like could be used toconstruct the layers of material 12 and that other methods could be usedto form the hexagonal channels 14, such as extrusion, machining ormolding, without departing from the spirit and scope of the invention.

In the first preferred embodiment, the internal surface area 16 iscoated with a desiccant material 20 which interacts with the fluid mediaflowing through the channels 14 to achieve water absorption from theair. In the first preferred embodiment, it is preferred that the core 64be used in connection with both the moisture transfer wheel 52 and theheat exchange wheel 54 and that the desiccant 20 be an exchange orsorbent material which exchanges or sorbs one of heat and mass with thefluid media flowing through the channels 14. That is, it is preferredthat the exchange or sorbent material be capable of removing mass ortransferring heat from the fluid media flowing through the channels 14and be capable of transferring mass or heat to the fluid media flowingthrough the channels 14. As used herein, the terms sorb and sorptivemean adsorption and/or absorption.

In the first preferred embodiment, it is preferred that the exchange orsorbent material be a desiccant material, such as a crystalline titaniumsilicate molecular sieve zeolite compound manufactured by EngelhardCorporation of Edison, N.J. under the trade name ETS and disclosed inU.S. Pat. No. 4,853,202, which is hereby incorporated by reference.

The use of channels having a cross section which is generally in theform of a hexagon is advantageous over other geometries, such assinusoidal, square, and triangular. The following is a brief explanationof why a hexagon is better than other geometries. For a more detailedexplanation, see U.S. patent application Ser. No. 08/246,548, filed May20, 1994, which is hereby incorporated by reference in its entirety.First, the theoretical available transfer surface area (i.e., based uponstandard measurements and calculations of the geometries prior tocoating the interactive material) of a hexagon is greater than thetransfer surface area of a sinusoidal, triangle or square for a givenvolume.

Second, the practical available transfer surface area (i.e., based uponstandard measurements and calculations of the geometries after coatingof the interactive material) of a hexagon is relatively greater, ascompared to theoretical calculations, than the transfer surface area ofa sinusoidal, triangle or square for a given volume because there areless surface area losses due to corner buildup. It is generally knownthat sorbent mass transfer is analogous to heat transfer. Thisrelationship is defined in U.S. Pat. No. 5,148,374, which is herebyincorporated by reference, as the number of transfer units whichcorresponds to the effectiveness of the heat transfer. The greater thenumber of transfer units, the more effective the heat transfer. Thenumber of transfer units is dependent on, among other things, theavailable transfer surface area. By minimizing corner build up, the core64 of the present invention achieves a number of transfer units which isequal to or greater than the number of transfer units the prior artcores achieve.

Third, the pressure drop through the core 64 of the present invention issignificantly less than the core constructed of the geometries mentionedabove because there is virtually no buildup in the corners of thegenerally hexagon shaped channels 14. Hence, the power necessary toforce the fluid media through the core 64 is significantly less thanthat needed to force the fluid media through the prior art cores. Forinstance, in the case of gas heated hybrid desiccant air-conditioningsystems, the reduction in power requirements allows the desiccantsystems to operate at the same cost as conventional CFC air-conditioningsystems for the same output of BTU's, without the inherent risk to theenvironment presented by CFC air-conditioning systems.

Fourth, the hexagonal core 64 provides much better bonding betweenchannels or cells compared to the wound corrugated process described inthe aforementioned patent application. Thus, the possibility for leakageof either fluid from one stream to the other at the sealing points isgreatly reduced.

While in the present invention it is preferred that the channels 14 beconfigured to be generally in the form of a hexagon in cross section, itis understood by those skilled in the art form this disclosure that thecross section of the channels could be other straight-sided shapes withequal angles and equal side lengths, such that the cross sectionapproaches a circle, and which permit the channels to be closelyadjoined to maximize the greatest transfer surface area per unit volumewithout departing from the spirit and scope of the invention. Althoughit is also understood by those skilled in the art from this disclosurethat other geometries could be used, such as, triangle, square,sinusoidal, so long as the operating parameters described below areattained, without departing from the scope and spirit of the invention.

The preferred method of making the core 64 comprises forming theplurality of adjoining channels 14 such that the channels 14 aregenerally in the form of a hexagon in cross section. As is describedabove, each of the channels 14 has a centrally disposed longitudinalaxis 18. The internal surface area 16 of the channels 14 is then coatedwith a suspension of the zeolite in water. After coating, thesubstrate/coating is dried to remove the water and provide zeoliteadhered to the substrate. The coating of the internal surface area 16 ofthe channels 14 with the zeolite 20 is accomplished by forced flowpassing of the zeolite 20, as suspended in water with silicate, throughthe channels 14 at a laminar flow rate. The coating of surfaces usingforced-flow passing is well understood by those of ordinary skill in theart and, therefore, further description thereof is omitted for purposesof convenience only. However, it is also understood by those skilled inthe art from this disclosure that the suspension of zeolite 20 could beapplied to the internal surface area 16 of the channels 14 in othermanners. For instance, the zeolite 20 could be applied, in a suspensionform, to the internal surface area 16 by deposition, wherein thesuspension is passed through the core 64 using a non-flooding technique.Alternatively, the zeolite 20 could be applied to the layers of material12 prior to assembling the layers of material 12 into the generallyhexagonal channels 14 or the zeolite 20 could be incorporated in thematerial which makes up the layers of material 12. Although it ispreferred for reasons of safety and economy to use water as thesuspension medium, organic solvents or mixtures of organic solvent(s)with water may also be employed.

Referring now to FIGS. 4 through 6, there is shown the moisture transferwheel 52 having the core 64 disposed therein. The layers of material 12which form the channels 14 of the core 64 provide the core 64 withsufficient structural integrity for most size wheels to avoid therequirement of a hub assembly and spokes, and thus in a preferredembodiment, as shown in FIG. 4, there is no hub assembly or spokes.

The rim 34 has a radially outwardly extending track 36 on its externalsurface. The track 36 allows the moisture transfer wheel 52 to besupported at its periphery, and then rotatably mounted within thehousing 38, as shown in FIG. 4. The housing 38 is generally in the formof a parallelepiped and includes a pair of semi-circular openings 40 oneach side to allow the moisture transfer wheel 52 to be placed in thesystem 10 in alignment with the process and regenerative sides. Aplurality of support wheels 42 are disposed within the housing 38 andare in rolling engagement with the track 36. The support wheels 42 arepositioned to rotatably support the moisture transfer wheel 52 in thehousing 38 such that the core 64 of the moisture transfer wheel 52 is inalignment or registry with the semicircular openings 40. As shown inFIG. 6, the support wheels 42 are supported within the housing 38 by agenerally T-shaped support member 44 which permits the support wheel 42to rotate with respect to the support member 44 in a manner wellunderstood by those of ordinary skill in the art. The particular mannerin which the support wheels 42 are supported within the housing 38 isnot pertinent to the present invention. A drive mechanism (not shown) isdisposed within the housing 38 and drivingly engages the exterior of therim 34 to rotate the moisture transfer wheel 52 with respect to thehousing 38.

The components of the housing 38 are preferably constructed of ahigh-strength, lightweight material, such as aluminum. However, it isunderstood by those skilled in the art from this disclosure that thehousing 38 could be constructed of other materials, such as a polymericmaterial or stainless steel, without departing from the spirit and scopeof the invention.

The details of the mounting and driving of the moisture transfer wheel52 within the housing 38 are not pertinent to the present invention. Itis recognized by those of ordinary skill in the art from this disclosurethat the moisture transfer wheel 52 can be mounted in any manner withoutdeparting from the spirit and scope of the invention. Accordingly,further description thereof is omitted for purposes of convenience only,and is not limiting.

Referring now to FIG. 2, the system 10 includes a first compressor 66having a suction side 66a in fluid communication with a first side 50aof the first pre-cool evaporator coil 50 and a discharge side 66b influid communication with a first side 60a of the first condenser coil60. More particularly, the suction side 66a of the first compressor 66is in fluid communication with the first side 50a of the first pre-coolevaporator 50 via a first conduit 68 and the discharge side 66b of thefirst compressor 66 is in fluid communication with the first side 60a ofthe first condenser coil 60 via a second conduit 70. A second side 50bof the first pre-cool evaporator coil 50 is in fluid communication witha second side 60b of the first condenser coil 60, as described in moredetail hereinafter.

The first conduit 68 includes a first crank case pressure regulator 72which senses the pressure on the suction side 66a of the firstcompressor 66. That is, the position of the first crank case pressureregulator 72 (i.e., open or closed) is responsive to the pressure of therefrigerant fluid within the first conduit 68, for the reasons describedhereinafter.

The system 10 further includes a second condenser coil 74 positionedbetween the second zone 52b of the moisture transfer wheel 52 and theambient space such that the regenerative air 58 passes through thesecond condenser coil 74. The second condenser coil 74 includes a firstside 74a in fluid communication with the second side 60b of the firstcondenser coil 60 and a second side 74b in fluid communication with thesecond side 50b of the first pre-cool evaporator 50. The second side 60bof the first condenser coil 60 is in fluid communication with the firstside 74a of the second condenser coil 74 via a third conduit 76 and thesecond side 74b of the second condenser coil 74 is in fluidcommunication with the second side 50b of the first pre-cool evaporatorcoil 50 via a fourth conduit 78, in a manner well understood by thoseskilled in the art.

As best shown in FIG. 2, the first condenser coil 60 is divided intofirst and second coil sections 60' and 60". The first coil section 60'has a first side 60a' in fluid communication with the discharge side 66bof the first compressor 66 via the second conduit 70. The first coilsection 60' of the first condenser coil 60 includes a second side 60b'in fluid communication with a first side 60a" of the second coil section60" via a fifth conduit 80. The second coil section 60" has a secondside 60b" in fluid communication with the second side 50b of the firstpre-cool evaporator 50 through the third conduit 76, second condensercoil 74 and fourth conduit 78.

In the first preferred embodiment, the first coil section 60' is spacedfrom the second coil section 60" by an air gap 82 to minimize heattransfer between the first and second coil sections 60', 60". Moreparticularly, the first coil section 60' is comprised of a single rowcoil wherein the tubes of the coil are thermally connected together by aplurality of thin, thermally conductive fin sheets (only one is shown)84, in a manner well understood by those skilled in the art. Similarly,the second coil section 60" is comprised of a coil having three rows oftubes thermally connected together by a plurality of thin, thermallyconductive fin sheets (only one is shown) 84, also in a manner wellunderstood by those skilled in the art. The air gap 82 exists betweenthe fin sheets of the first and second coil sections 60', 60".

By separating the first condenser coil 60 into the first and second coilsections 60', 60", heat transfer between the first and second coilsections 60', 60" is minimized. That is, the separation of the first andsecond coil sections 60', 60" eliminates heat transfer from the firstcoil section 60' to the second coil section 60" through the fin sheets,thereby minimizing the averaging effect described above, and allowingthe first coil section 60' to be as hot as possible and the air flowingfrom the first condensing coil to be as hot as possible.

As can be seen from FIG. 2, since the first coil section 60" only has asingle row of tubes and the second coil section 60" has three rows oftubes, the surface transfer area of the first coil section 60' is lessthan the surface transfer area of the second coil section 60". The firstcoil section 60' is positioned between the second zone 52b of themoisture transfer wheel 52 and the second coil section 60" so that theregenerative air 58 flowing across the first coil section 60' is superheated by the refrigerant fluid flowing directly from the discharge side66b of the first compressor 60 through the second conduit 70. It ispreferred that the first coil section 60' be positioned downstream fromthe second coil section 60" and that the first coil section 60' be indirect fluid communication with the first compressor 66, because itallows the regenerative air 58 flowing across the first condensing coil60 to see the first coil section 60' last. Since the first coil section60' is hotter than the second coil section 60" (because the air gap 82prevents the averaging effect described above), the regenerative air 58flowing into the moisture transfer wheel 52 can be at higher temperaturethan with the use of conventional condensing coils, without increasingthe temperature of the refrigerant fluid flowing through the coil.

While in the first preferred embodiment, it is preferred that the firstcoil section 60' and the second coil section 60" be comprised of one andthree rows of tubes, respectively, it is understood by those of ordinaryskill in the art from this disclosure that the present invention is notlimited to any particular number of rows of tubes in either the first orsecond coil sections 60', 60" and that the first condenser coil 60 canbe divided into more than two sections. With respect to the spacing orair gap between the first and second coil sections 60', 60", the spacingis sized to minimize the transfer of heat between the first and secondcoil sections 60', 60" (i.e., to prevent the relatively lowertemperature of the second coil section 60" from lowering the relativelyhigher temperature of the first coil section 60'), and yet allows thefirst condensing coil 60 to be positioned between the second zones 52b,54b of the moisture transfer wheel 52 and heat exchange wheel 54.

In the first preferred embodiment, the second condenser coil 74 is alsodivided into first and second coil sections 74', 74", in the same mannerthat the first condensing coil 60 is divided into first and second coilsections 60', 60". For purposes of brevity, the second condensing coil74 in FIG. 2 has been marked with element numerals which correspond tothe element numerals of the description of the first condensing coil 60without the accompanying description herein. It is believed that areading of the description of the first condensing coil 60 incombination with viewing the element numerals in FIG. 2 of the secondcondensing coil 74 provide a sufficient understanding of the secondcondenser coil 74. However, the second condenser coil 74 is differentfrom the first condensing coil 60 in one respect. That is, a hold-backvalve 86 is disposed between the first and second coil sections 74', 74"in the sixth conduit 88 extending therebetween and the first coilsection 74' is located upstream from the second coil section 74". Thepurpose of the hold-back valve 86 is described hereinafter. By locatingthe first coil section 74' closest to the moisture transfer wheel 52, itsees the coolest air from the moisture transfer wheel 52 to ensure thatall of the fluid that flows through the first coil section 74' iscondensed, as described in more detail below.

By locating the second condensing coil 74 downstream from the moisturetransfer wheel 52, the relatively cool air exiting the moisture transferwheel 52 is used to condense any refrigerant that has not been condensedby the first condensing coil 60. This is a unique and efficient mannerto achieve pre-cooling of the process air 51 entering the moisturetransfer wheel 52 when the wet bulb temperature of the ambient air isgreater than 74 degrees F.

While it is preferred that the first and second condensing coils 60, 74be separated into the first and second coil sections 60',74',60",74", itis understood by those of ordinary skill in the art from this disclosurethat the pre-cooling of the process air 51 could be attained even if thefirst and second condensing coils 60, 74 where constructed of a singlecoil or section.

As shown in FIG. 2, the system 10 further includes a refrigeration fluidreceiver 90 in fluid communication with the second side 60b of the firstcondenser coil 60 and the second side 50b of the first pre-coolevaporator coil 50. More particularly, a seventh conduit 92 extendsbetween the outlet side 90a of the receiver 90 and the fourth conduit 78which is in fluid communication with the first pre-cool evaporator coil50. An eighth conduit 94 extends between the inlet side 90b of thereceiver 90 and the third conduit 76, which is fluid communication withthe second side 60b of the first condenser coil 60. The eighth conduit94 includes a pressure regulator valve 96 which senses the pressure ofthe refrigerant fluid within the receiver 90. When the pressure of therefrigerant fluid within the receiver 90 falls below a predeterminedvalue, the pressure regulator valve 96 opens to allow refrigerant fluidwithin the first condenser coil 60 to flow into the receiver 90, asdescribed in more detail hereinafter. It is preferred that the receiver90 be in fluid communication with the second side 60b of the firstcondensing coil 60, as oppose to the second conduit 70 which wouldresult in diverting needed hot refrigerant fluid away from the firstcondensing coil 60.

The system 10 further includes a second compressor 98 in parallel withthe first compressor 66. The second compressor 98 includes a suctionside 98a in fluid communication with the first side 50a of the firstpre-cool evaporator coil and a discharge side 98b in fluid communicationwith the first side 60a of the first condenser coil 66. Moreparticularly, a ninth conduit 100 extends between the suction side 98aof the second compressor 98 and the first conduit 68 which is in fluidcommunication with the first side 50a of the first pre-cool evaporatorcoil 50. A tenth conduit 102 extends between the discharge side 98b ofthe second compressor 98 and the second conduit 70 which is in fluidcommunication with the first side 60a of the first condensing coil 60.

The first compressor 66 is sized to provide sufficient energy topre-cool the process air 51 when the wet bulb temperature of the processair 51 is between 70 and 74 degrees Fahrenheit. The second compressor 98is sized to provide sufficient energy, in combination with the firstcompressor 66, to pre-cool the process air 51 when the wet bulbtemperature of the process air 51 is greater than 74 degrees Fahrenheit,as described in more detail hereinafter. Using two different sizedcompressors is more energy efficient than one large compressor when thewet bulb temperature is less than 74 degrees Fahrenheit and since a wetbulb temperature of greater than 74 degrees Fahrenheit does not occurregularly, the full use of a large compressor would also not occuroften. While it is preferred that two compressors be used to achieve theappropriate amount of pre-cooling, it is understood by those of ordinaryskill in the art from this disclosure that any number of compressorscould be used, including one, three or four, without departing from thespirit and scope of the invention.

As mentioned above, the system 10 includes a hold-back valve 86. Thehold-back valve 86 is positioned between the first side 74a of thesecond condenser 74 and the first pre-cool evaporator 50. The hold-backvalve 86 is responsive to a pressure of the refrigerant fluid within atleast a portion of the second condenser 74 such that the hold-back valve86 is open when the pressure of the refrigerant fluid within the portionof the second condenser 74 is above a predetermined pressure and thehold-back valve 86 is closed when the pressure of the refrigerant fluidwithin the portion of the second condenser 74 is below the predeterminedpressure. More particularly, and as mentioned above, the hold-back valve86 is in fluid communication with and is positioned between the firstand second coil sections 74', 74" of the second condensing coil 74. Thatis, the sixth conduit 88 includes the hold-back valve 86. The portion ofthe second condenser coil 74 which is being sensed by the hold-backvalve 86 is the second coil section 74".

In the first preferred embodiment, the system 10 further includes asecond pre-cool evaporator coil 104 positioned between the firstpre-cool evaporator coil 50 and the first zone 52a of the moisturetransfer wheel 52. The second pre-cool evaporator coil 104 includes afirst side 104a which is in fluid communication with the suction side98a of the second compressor 98 and the suction side 66a of the firstcompressor 66 via an eleventh conduit 106 which is in fluidcommunication with the first conduit 68. The second pre-cool evaporatorcoil 104 includes a second side 104b in fluid communication with thesecond side 74b of the second condenser coil 74 via a twelfth conduit108 which is in fluid communication with the fourth conduit 78.

The receiver 90 is also in fluid communication with the second side 74bof the second condenser coil 74 so that the first pre-cool evaporator 50can receive refrigerant fluid from the fluid receiver 90 when thehold-back valve 86 is closed, as described in more detail hereinafter.

The system 10 further includes a recovery evaporator coil 110 positionedbetween the second zone 52b of the moisture transfer wheel 52 and theambient space such that the regenerative air 58 passes through therecovery evaporator coil 110. More particularly, the recovery evaporatorcoil 110 is positioned downstream of the second condenser coil 74 andincludes a first side 110a in fluid communication with the suction sides66a, 98a of the first and second compressors 66, 98, and a second side110b in fluid communication with the second side 60b of the firstcondenser coil 60. More particularly, a thirteenth conduit 112 extendsbetween the first side 110a of the recovery evaporator coil 110 and thefirst conduit 68. The thirteenth conduit 112 includes a crank casepressure regulator 114 for sensing the pressure of refrigerant fluidwithin the first conduit 68, for reasons described hereinafter. Afourteenth conduit 116 extends from the second side 110b of the recoveryevaporator coil 110 and is in fluid communication with the fourthconduit 78 which is in fluid communication with the second side 74b ofthe second condensing coil 74 and the outlet 90a of the receiver 90 viathe seventh conduit 92. As such, the recovery evaporator coil 110 andthe first pre-cool evaporator coil 50 are arranged in parallel betweenthe first condenser coil 60 and the first compressor 66.

The second side 50b, 104b, 110b, of each of the first pre-coolevaporator coil 50, second pre-cool evaporator coil 104 and recoveryevaporator coil 110 are in fluid communication with an expansion valvewhich affects a pressure drop of the refrigerant fluid flowing into therespective coil and a solenoid valve, commonly designated 50c, 104c, and110c, respectively. The solenoid valves are used to control the flow ofrefrigerant fluid into the respective coils in accordance with theoperation of the system 10, as described hereinafter. The solenoidvalves are standard, electrically operated, off-the-shelf items wellunderstood by those skilled in the art, accordingly, further descriptionthereof is omitted for purposes of convenience only, and is notlimiting.

In the first preferred embodiment, the system 10 senses the wet-bulbtemperature of the process air 51 entering the system 10 through the useof an enthalpy sensor 118 located just upstream from the first pre-coolevaporator coil 50. Enthalpy sensors are well known to those of ordinaryskill in the art, accordingly, further description thereof is omittedfor purposes of convenience only, and is not limiting. The position ofthe solenoid valves 50c, 104c, 110c and the selection of which of thefirst and second compressors 66, 98 is operating are controlled by amicroprocessor (not shown) in response to the wet bulb temperature ofthe process air 51 sensed by the enthalpy sensor 118, as describedbelow. It is also understood by those skilled in the art from thisdisclosure that other methods could be used to sense the wet-bulbtemperature of the process air 51 just prior to entering the firstpre-cool evaporator coil 50. For instance, the second compressor 98could be controlled in response to the load on the first compressor 66.That is, if the pressure within the first compressor 66 is above apredetermined value, the second compressor 98 could automatically beginoperation.

Referring now to FIG. 7, there is shown a second preferred embodiment ofa hybrid air-conditioning system 10 in accordance with the presentinvention. The system 10 in accordance with the second preferredembodiment is very similar to the first preferred embodiment, except forthe following differences. The second compressor 98, second condensercoil 74 and second pre-cool evaporator coil 104 are fluidly coupled inan independent standard heat pump configuration. Similarly, the firstcompressor 66, first condenser coil 60, first pre-cool evaporator coil50 and recovery evaporator coil 110 are fluidly coupled together as anindependent circuit. The following is a brief description of the system10 in accordance with the second preferred embodiment.

Referring now to FIG. 7, the discharge side 66b of the first compressor66 is in fluid communication with the first condenser coil 60 via thesecond conduit 70. The first condensing coil 60 of the second preferredembodiment is identical to the first condensing coil 60 of the firstpreferred embodiment. The second side 50b of the first pre-coolevaporator coil 50 is in fluid communication with the second side 60b ofthe first condensing coil 60 via the third conduit 76. The second side110b of the recovery evaporator coil 110 is also in fluid communicationwith the second side 60b of the first condensing coil 60 via thefourteenth conduit 116 and the third conduit 76. The first side 50a ofthe first pre-cool evaporator coil 50 is in fluid communication with thesuction side 66a of the first compressor 66 via the first conduit 68which includes a crank case pressure regulator 72. The first side 110aof the recovery evaporator coil 110 is in fluid communication with thesuction side 66a of the first compressor 66 via the thirteenth conduit112 which is in fluid communication with the first conduit 68.

The discharge side 98b of the second compressor 98 is in fluidcommunication with the first side 74a of the second condensing coil 74.The second condensing coil 74 of the second preferred embodiment isidentical to the second condensing coil 74 of the first preferredembodiment, except that the hold-back valve 86 is omitted. The secondside 104b of the second pre-cool evaporator coil 104 is in fluidcommunication with the second side 74b of the second condensing coil 74via the twelfth conduit 108. The first side 104a of the second pre-coolevaporator coil 104 is in fluid communication with the suction side 98aof the second compressor 98 via the ninth conduit 100.

Referring now to FIG. 8, there is shown a third preferred embodiment ofa hybrid air-conditioning system 10 in accordance with the presentinvention. The system 10 in accordance with the third preferredembodiment is very similar to the second preferred embodiment, exceptfor the following differences. The second condensing coil 74 is dividedinto first and second coil sections 74' and 74". The first coil section74' has a first side 74a' in fluid communication with the discharge side98b of the second compressor 98. The first coil section 74' of thesecond condenser coil 74 includes a second side 74b' in fluidcommunication with a first side 74a" of the second coil section 74" viaa sixth conduit 88. The second coil section 74" has a second side 74b"in fluid communication with the second side 104b of the second pre-coolevaporator 104 through the twelfth conduit 108. The first coil section74' of the first condenser coil 74 is located between the first coilsection 60' of the first condenser coil 60 and the second zone 52b ofthe moisture transfer wheel 52. The following is a brief description ofthe system 10 in accordance with the third preferred embodiment.

With respect to FIG. 8, the discharge side 66b of the first compressor66 is in fluid communication with the first condenser coil 60 via thesecond conduit 70. The first condensing coil 60 of the third preferredembodiment is identical to the first condensing coil 60 of the firstpreferred embodiment. The second side 50b of the first pre-coolevaporator coil 50 is in fluid communication with the second side 60b ofthe first condensing coil 60 via the third conduit 76. The second side110b of the recovery evaporator coil 110 is also in fluid communicationwith the second side 60b of the first condensing coil 60 via thefourteenth conduit 116 and the third conduit 76. The first side 50a ofthe first pre-cool evaporator coil 50 is in fluid communication with thesuction side 66a of the first compressor 66 via the first conduit 68which includes a crank case pressure regulator 72. The first side 110aof the recovery evaporator coil 110 is in fluid communication with thesuction side 66a of the first compressor 66 via the thirteenth conduit112 which is in fluid communication with the first conduit 68.

The discharge side 98b of the second compressor 98 is in fluidcommunication with the first side 74a of the second condensing coil 74.The second condensing coil 74 of the third preferred embodiment isseparated into first and second coil sections 74' and 74", similar tothe first and second embodiments; however, the first coil section 74' ofthe second condenser coil 74 is positioned between the first condensercoil 60' and the second zone 52b of the moisture transfer wheel 52. Thefirst coil section 74' of the second condenser coil 74 is separated byan air gap from the first coil section 60' of the first condenser coil60 to minimize heat transfer between coils 60 and 74. The second coilsection 74" of the second condenser coil 74 is positioned between thesecond zone 52b of the moisture transfer wheel 52 and the ambient spacesuch that the regenerative air 58 passes through the first and secondcoil sections 74' and 74" of the second condenser coil 74. The secondside 104b of the second pre-cool evaporator coil 104 is in fluidcommunication with the second side 74b of the second condensing coil 74via the twelfth conduit 108. The first side 104a of the second pre-coolevaporator coil 104 is in fluid communication with the suction side 98aof the second compressor 98 via the ninth conduit 100.

With respect to FIG. 2, the system 10 is operated to control thecondition of air in the enclosed space when the wet bulb temperature ofthe process air 51 in the ambient space (i.e., the process air 51 whichenters the system 10) is greater than seventy-four degrees Fahrenheit,by rotating the moisture transfer and heat exchange wheels 52, 54 in amanner well-understood by those skilled in the art, and as described inU.S. Pat. No. 5,148,374, which is incorporated herein by reference.While the moisture transfer and heat exchange wheels 52, 54 arerotating, the first and second compressors 66, 98 are operated to passrefrigerant fluid from the first and second compressors 66, 98 throughthe first condenser coil 60, second condenser coil 74, first pre-coolevaporator 50, second pre-cool evaporator 104 and back to the first andsecond compressors 66, 98 such that the process air 51 between thesecond pre-cool evaporator 104 and the first zone 52a of the moisturetransfer wheel 52 has a dry-bulb temperature of less than or equal toabout seventy degrees Fahrenheit.

More particularly, as the refrigerant fluid passes from the first andsecond compressors 66, 98, it is partially condensed in the firstcondenser coil 60, with a majority of the condensing occurring in thefirst coil section 60'. The refrigerant fluid then flows from the firstcondenser coil 60 to the second coil section 74" of the secondcondensing coil 74. As the refrigerant fluid exits the second coilsection 74" of the second condensing coil 74, it is fully condensed. Assuch, the hold-back valve 86, which is sensing the pressure of therefrigerant fluid as it exits the second coil section 74" of the secondcondensing coil 74, remains open and the refrigerant fluid passes to thefirst coil section 74' of the second condensing coil 74. Any flashing ofrefrigerant fluid that occurs as the refrigerant fluid flows through thehold-back valve 86, is condensed in the first coil section 74' of thesecond condensing coil 74. With the solenoid valves 50c, 104c of thefirst and second pre-cool evaporator coils 50, 104 in the open position,and the solenoid valve 110c of the recovery evaporator 110 in the closedposition, the refrigerant fluid flows from the second side 74b of thesecond condensing coil 74 to the first and second pre-cool evaporatorcoils 50, 104 through the fourth conduit 78 and twelfth conduit 108. Therefrigerant fluid then flows from the first and second pre-coolevaporator coils 50, 104 in a relatively low temperature and pressurevapor form to the suction sides 66a, 98a of the first and secondcompressors 66, 98. The first crank case pressure regulator 72 remainsopen so long as the pressure of the refrigerant fluid on the suctionsides 66a, 98a of the first and second compressors 66, 98 remains belowa predetermined value for the purpose of not overloading thecompressors. If the pressure of the refrigerant fluid on the suctionsides 66a, 98a of the first and second compressors 66, 98 exceeds thepredetermined value, the regulator 72 will partially close to throttlethe flow of refrigerant to the first and second compressors 66, 98. Theregulator 114 operates in a similar manner as anyone skilled in the artunderstands.

In operating the system 10, it is desired to control the fans 56, 62 toachieve a high normal air-flow velocity through the system 10.Preferably, the nominal air-flow velocity is about two hundred to abouteight hundred feet per minute (FPM), and, more preferably, about fourhundred to about five hundred FPM. After the process air 51 having awet-bulb temperature of 74 degrees F. or greater flows across and thenexits from the first and second pre-cool evaporator coils 50, 104 it hasa dry-bulb temperature of about 71 degrees F. After the process air 51emerges from the first zone 52a of the moisture transfer wheel 52, ithas a dry-bulb temperature of about 105 to 120 degrees F. As the processair 51 emerges from the first zone 54a of the heat exchange wheel 54, ithas a dry-bulb temperature of about 70 to 85 degrees F. Similarly, theregenerative air 58 enters the second zone 54b of the heat exchangewheel 54 at a dry-bulb temperature in the range of about 65 to 80degrees F. after the regenerative air leaves the evaporator pad 61. Theregenerative air 58 exits the second zone 54b of the heat exchange wheel54 at a dry-bulb temperature of about 100 to 115 degrees F. As theregenerative air 58 flows across the first condensing coil 60, thedry-bulb temperature of the regenerative air 58 is raised to about 130to 145 degrees F. and preferably 140 degrees F. The regenerative air 58then passes through the second zone 52b of the moisture transfer wheel52 and exits therefrom at a dry-bulb temperature of about 90 to 100degrees F. The regenerative air 58 then flows across the secondcondensing coil 74, which raises its dry-bulb temperature to about 120to 130 degrees F.

Operation of the second preferred embodiment of the system 10, shown inFIG. 7, when the wet-bulb temperature of the process air 51 entering thesystem 10 is greater than seventy-four degrees Fahrenheit is generallyidentical to that described above in connection with the first preferredembodiment. That is, the solenoid valves 50c, 104c for the first andsecond pre-cool evaporator coils 50, 104 are open while the solenoidvalve 110c of the recovery evaporator coil 110 is closed. In thismanner, the second compressor 98, second condensing coil 74 and secondpre-cool evaporator coil 104 operate in the manner of a standard heatpump. The first compressor 66, first condensing coil 60, first pre-coolevaporator coil 50 operate in the same manner as that described above,except that the refrigerant fluid does not flow through the secondpre-cool evaporator coil 104 or the second condensing coil 74.

Placement of the first pre-cool evaporator 50 ahead of the secondpre-cool evaporator 104 minimizes the compressor compression ratios(absolute discharge pressure/absolute suction pressure) and increasesefficiency. Because the process air 51 is warmer before it enters thefirst pre-cool evaporator coil 50, the temperature of the refrigerantfluid entering the suction side 66a of the first compressor 66 can behigher than the temperature of the refrigerant entering the suction side98a of the second compressor 98. For example, in operation thetemperature and pressure of the refrigerant at the suction sides 66a and98a of the first and second compressors 66, 98 are 65 degrees F., 124PSIA and 55 degrees F., 110 PSIA, respectively. The first condensingcoil 60, which is located before the second zone 52b of the moisturetransfer wheel 52 needs to operate at a higher condensing temperature(140 degrees F., 350 PSIA) than the second condensing coil 74 (120degrees F., 275 PSIA), which is located after the second zone 52b of themoisture transfer wheel 52. Therefore, the compression ratio isminimized and the system efficiency is increased by having the firstpre-cool evaporator 50 with the highest temperature refrigerant fluid aspart of the same closed system as the first condensing coil 60 with thehighest condensing temperature. This yields a compression ratio for thefirst compressor 66 of 2.8 (350 PSIA/124 PSIA) and a compression ratiofor the second compressor of 2.5 (275 PSIA/110 PSIA) (versus 3.2 (350PSIA/110 PSIA) for the first compressor 66 if the positions of the firstand second pre-cool recovery evaporators 50 and 104 were reversed).

Operation of the third preferred embodiment of the system 10, shown inFIG. 8, when the wet-bulb temperature of the process air 51 entering thesystem 10 is greater than seventy-four degrees Fahrenheit is generallyidentical to that described above in connection with the secondpreferred embodiment. However, as the regenerative air 58 flows acrossthe first condensing coil 60, the dry-bulb temperature of theregenerative air 58 is raised to about 130 to 145 degrees F. andpreferably 140 degrees F. The regenerative air then passes through thefirst coil section 74' of the second condenser coil 74 to furtherincrease the regenerative air 58 temperature or to maintain the sameleaving air temperature and operate at a lower condensing temperature,improving the compressor's efficiency. The regenerative air 58 thenpasses through the second zone 52b of the moisture transfer wheel 52 andexits therefrom at a dry-bulb temperature of about 90 to 100 degrees F.The regenerative air 58 then flows across the second coil section 74" ofthe second condensing coil 74, which raises its dry-bulb temperature toabout 120 to 130 degrees F. Placement of the first pre-cool evaporator50 ahead of the second pre-cool evaporator 104 still minimizes thecompressor compression ratios (absolute discharge pressure/absolutesuction pressure) and increases efficiency in a similar manner to thatdescribed above in connection with the second embodiment even though thefirst coil section 74' of the second condenser coil 74 is located on theupstream side of the moisture transfer wheel 52. The larger relativesize of the second coil section 74" in comparison to the first coilsection 74' of the second condenser coil 74 allows the second condensercoil 74 to operate at a lower condensing temperature in comparison tothe first condenser coil 60.

With respect to the first preferred embodiment, when the wet-bulbtemperature of the process air 51 in the ambient space is betweenseventy and seventy-four degrees Fahrenheit, the system 10 is operatedin a manner generally similar to that described above, except that thesecond condenser 74, second pre-cool evaporator coil 104 and secondcompressor 98 are not operating. That is, the solenoid valves 104c, 110cof the second pre-cool evaporator coil 104 and recovery evaporator coil110 are closed and the solenoid valve 50c of the first pre-coolevaporator coil 50 is open. As refrigerant fluid flows through the firstcondensing coil 60, it is almost entirely condensed. As such, thehold-back valve 86 will sense the drop in pressure of the refrigerantfluid in the second coil section 74" of the second condensing coil 74,and close. Once the hold-back valve 86 is closed, refrigerant fluidwithin the second coil section 74" of the second condensing coil 74begins to back up toward the first condensing coil 60. Similarly, sincethe first pre-cool evaporator coil 50 can no longer draw refrigerantfluid from the second condensing coil 74, it begins to draw condensedrefrigerant fluid from the receiver 90. This will result in the pressureof the refrigerant fluid within the receiver 90 falling below apredetermined value thereby causing the pressure regulator valve 96 toopen. With the pressure regulator valve 96 open, the condensed fluidfrom the first condensing coil 60 flows directly to the receiver 90.

It is only necessary to use the first condensing coil 60, firstcompressor 66 and first pre-cool evaporator coil 50 because when theprocess air 51 has a wet-bulb temperature of between seventy-four andseventy degrees Fahrenheit, the first condensing coil 60 and firstpre-cool evaporator coil 50 are all that is necessary to bring thewet-bulb temperature of the process air 51 entering the system 10 to adry-bulb temperature of seventy degrees Fahrenheit. Therefore, thesystem 10 can operate in a more energy-efficient manner when thetemperature of the process air 51 is in this range.

With respect to the second preferred embodiment of FIG. 7, the secondcompressor 98, second condensing coil 74 and second pre-cool evaporatorcoil 104 are simply not operating when the wet-bulb temperature of theprocess air 51 entering the system is between seventy-four and seventydegrees Fahrenheit. Similarly, the solenoid valve 110c of the recoveryevaporator coil 110 is closed while the solenoid valve 50c of the firstpre-cool evaporator coil 50 is open. In this manner, the refrigerantfluid flows through the first compressor 66, first condensing coil 60and first pre-cool evaporator coil 50, generally in a manner which issimilar to that described above in connection with the first preferredembodiment.

With respect to the third preferred embodiment of FIG. 8, when thewet-bulb temperature of the process air 51 in the ambient space isbetween seventy and seventy-four degrees Fahrenheit, the system 10 isgenerally operated in a manner identical to that described above inconnection with the second preferred embodiment.

Referring now to FIG. 2, when it is necessary to control the humidity ofair in the enclosed space when the wet-bulb temperature of the processair 51 in the ambient space is less than seventy degrees Fahrenheit, thefirst compressor 66 passes refrigerant fluid through the firstcondensing coil 60, the first pre-cool evaporator 50 and the recoveryevaporator coil 110 and back to the first compressor 66. Thus, thesolenoid valves 50c, 110c of the first pre-cool evaporator coil 50 andrecovery evaporator coil 110, respectively, are open while the solenoidvalve 104c of the second pre-cool evaporator coil 104 is closed. In thismode, the hold-back valve 86 is closed, but the first pre-coolevaporator coil 50 cannot completely evaporate the refrigerant flowingtherethrough because of the reduced load provided by the lowertemperature process air 51 entering the system 10. As such, the recoverycoil 110 assists in completely evaporating the refrigerant fluid flowingfrom the first condensing coil 60 to the first compressor 66. Therefore,the first pre-cool evaporator coil 50 only does a small amount ofcooling of the process air 51 flowing therethrough, and the majority ofthe evaporation occurs in the recovery evaporator coil 110. While littleor no pre-cooling of the process air 51 flowing into the system 10 isnecessary to dehumidify the enclosed space when the wet-bulb temperatureof the processor 51 is below seventy degrees Fahrenheit, the firstcondensing coil 60 is still used to raise the temperature of theregenerative air 58 entering the second zone 52b of the moisturetransfer wheel 52 to one-hundred-and-forty degrees Fahrenheit or above.Thus, the recovery evaporator coil 110 is needed to balance thecondensing done in the first condensing coil 60.

The second preferred embodiment of the system 10, shown in FIG. 7, isoperated in a similar manner to control the humidity in the air in theenclosed space when the wet-bulb temperature of the process air 51 isless than seventy degrees Fahrenheit. The first compressor 66 passesrefrigerant fluid through the first condensing coil 60, the firstpre-cool evaporator 50 and the recovery evaporator coil 110 and back tothe first compressor 66. Thus, the solenoid valves 50c, 110c of thefirst pre-cool evaporator coil 50 and recovery evaporator coil 110,respectively, are open. The second compressor 98, second condenser coil74 and second pre-cool evaporator coil 104 are not operating.

While it is preferred that the dry bulb temperature of the process air51 entering the first zone 52a of the moisture transfer wheel 52 be lessthan or equal to 70 degrees Fahrenheit, it is understood by thoseskilled in the art from this disclosure that the present invention isnot limited to pre-cooling the process air 51 to any particulartemperature since the preferred temperature of the process air 51entering the first zone 52a of the moisture transfer wheel 52 isdictated by the performance of the moisture transfer wheel 52. That is,for any moisture transfer wheel it is the temperature relationshipbetween the process air leaving the moisture transfer wheel and therequired regeneration temperature of the regeneration air entering themoisture transfer wheel, described above, which controls the preferredtemperature of the process air entering the moisture transfer wheel.

The third preferred embodiment of the system 10, shown in FIG. 8, isoperated in the same manner as the second embodiment to control thehumidity in the air in the enclosed space when the wet-bulb temperatureof the process air 51 is less than seventy degrees Fahrenheit.

From the foregoing description, it can be seen that the presentinvention comprises a hybrid air-conditioning system. It will beappreciated by those skilled in the art from this disclosure thatchanges could be made to the embodiments described above in theforegoing description without departing from the broad, inventiveconcepts thereof. Thus, the present invention is not limited to anyparticular manner of pre-cooling the process air 51 which enters thefirst zone 52a of the moisture transfer wheel 52. For instance, thepre-cool evaporator coils could be tied to a refrigeration system whichis not related to any other portion of the system 10 or another type ofcooling mechanism, such as water from a cooling tower, could be used topre-cool the process air 51. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but isintended to cover all modifications which are within the scope andspirit of the invention as defined by the appended claims.

I claim:
 1. A hybrid air-conditioning system for controlling thecondition of air in a building enclosed space comprising:first means forpassing process air from an ambient space through a first pre-coolevaporator coil, through a first zone of a rotatable moisture transferwheel and then through a first zone of a rotatable heat exchange wheelto an enclosed and conditioned space; second means for passingregenerative air from the enclosed and conditioned space through asecond zone of said heat exchange wheel, through a first condenser coil,through a second zone of said moisture transfer wheel and then to theambient space; a first compressor having a suction side in fluidcommunication with a first side of said first pre-cool evaporator coiland a discharge side in fluid communication with a first side of saidfirst condenser coil, a second side of said first pre-cool evaporatorcoil being in fluid communication with a second side of said firstcondenser coil; and a second compressor having a suction side in fluidcommunication with a first side of a second pre-cool evaporator coil anda discharge side in fluid communication with a first side of a secondcondenser coil, said second condenser coil having a second side in fluidcommunication with a second side of said second pre-cool evaporatorcoil, the second condenser coil having first and second coil sections,said first coil section of said second condenser coil being positionedbetween said first condenser coil and said second zone of said moisturetransfer wheel and said second coil section of said second condensercoil being positioned between said second zone of said moisture transferwheel and said ambient space such that the regenerative air passesthrough said first and second sections of said second condenser coil. 2.The hybrid air-conditioning system as recited in claim 1 wherein saidsecond pre-cool evaporator coil is positioned between said firstpre-cool evaporator coil and said first zone of said moisture transferwheel.
 3. The hybrid air-conditioning system as recited in claim 1wherein said first coil section of said second condenser coil has afirst side in fluid communication with said discharge side of saidsecond compressor and a second side in fluid communication with a firstside of said second coil section of said second condenser coil, saidsecond coil section of said second condenser coil having a second sidein fluid communication with said second side of said second pre-coolevaporator coil.
 4. The hybrid air-conditioning system as recited inclaim 1 wherein said first and second coil sections of said secondcondenser coil each have a surface transfer area, said surface transferarea of said first coil section of said second condenser coil being lessthan the surface transfer area of said second coil section of said firstcondenser coil.
 5. The hybrid air-conditioning system as recited inclaim 1 wherein said first condenser coil is divided into first andsecond coil sections, said first coil section of said first condensercoil having a first side in fluid communication with said discharge sideof said first compressor and a second side in fluid communication with afirst side of said second coil section of said first condenser coil,said second coil section of said first condenser coil having a secondside in fluid communication with said second side of said first pre-coolevaporator coil, said first coil section of said first condenser coilbeing spaced from said second coil section by an air gap to minimizeheat transfer between the first and second coil sections of said firstcondenser coil.
 6. The hybrid air-conditioning system as recited inclaim 5 wherein said first and second coil sections of said firstcondenser coil each have a surface transfer area, said surface transferarea of said first coil section of said first condenser coil being lessthan the surface transfer area of said second coil section of said firstcondenser coil.
 7. The hybrid air-conditioning system as recited inclaim 1 further comprising a recovery evaporator coil positioned betweensaid second zone of said moisture transfer wheel and said ambient spacesuch that the regenerative air passes through said recovery evaporatorcoil, said recovery evaporator coil having a first side in fluidcommunication with said suction side of said first compressor and asecond side in fluid communication with said second side of said firstcondenser, said first pre-cool and recovery evaporator coils beingarranged in parallel between said first condenser coil and said firstcompressor.
 8. A method of operating the hybrid air-conditioning systemof claim 1 for controlling the condition of air in the enclosed spacewhen the wet bulb temperature of the process air in the ambient space isgreater than 74 degrees F. comprising the steps of: rotating themoisture and heat transfer wheels while operating the first and secondcompressors to respectively pass refrigerant fluid from the first andsecond compressors through the first and second condenser coils, firstand second pre-cool evaporator coils and back to the first and secondcompressors such that process air entering the first zone of themoisture transfer wheel has a dry bulb temperature of less than or aboutequal to 70 degrees F.